There are numerous small machine parts, tools and the like which can be accurately formed by broaching operations. However, the capabilities of broaches for such machining operations have not been fully utilized. It is likely this is the result of many factors, but a few of these might be noted. One undoubtedly has been the fact that historically broaching machines were large heavy pieces of equipment with very substantial capacities for applying cutting forces between a broach and a workpiece. At least in some measure this resulted from a recognition that for the broaching operation to be satisfactorily performed an exact alignment between the broach and the workpiece must be maintained, i.e., deflections of one or both could not be tolerated as metal was removed by the broach. Another factor has undoubtedly been the overall speed of operation, i.e., the number of finished parts turned out in a given period of time. While the actual removal of metal by the broach can be quite rapid, there are significant rest times between each metal removing stroke which add up to an overall machine use which is not as great as might be desired. These rest times have been in a large measure the result of the necessity of changing workpieces. To some extent, they are also the result of the necessity of returning the broach to its original position before the start of the next metal removing phase.
The principal object of the present invention is to provide broaching machines which can be utilized for forming numerous small machine parts, tools, etc., at a relatively high rate of speed. An important phase of this is to reduce the size, bulk, of the machine. This results, among other things, in better utilization of factory space and in lowered acquisition costs. Stated another way, for a machine occupying a given amount of factory space, one incorporating the teachings of the present invention will produce more machining operations in a given period of time than will the conventional broaching machine. In the present invention this is accomplished by the contributions of two factors, namely, (1) the use of two broaches mounted in balanced arrangement on a single carriage, and (2) the use of two adjacent carriages each carrying broaches with the carriages being stroked alternately.
As to the first of these features, each broach supporting carriage in the present invention has ways at one pair of opposite sides thereof, with the broaches at a second pair of opposite sides and a centrally mounted ram. Thus the loads imposed on the carriage by the broaches are balanced at each side of the ways and at each side of the ram connection. This balancing of the loads results in the ability to reduce the sections of the members which make up the carriage, the ways, etc.; or, to put it another way, the deflection causing loads which must be resisted are not as serious as in the case with the conventional broaching machine. I am aware that there have been prior art broaching machines having a carriage which could be tooled on opposite sides, but such machines had the tooling cantilevered out on the carriage from a ways at one side only of the carriage. As a consequence, there was not the balancing of the broaching forces which must be resisted by the ways as is achieved by the present invention.
Insofar as the second feature is concerned, i.e., the alternate stroking of two adjacent carriages, this permits a single workpiece feeding apparatus to be utilized to feed two broaches. Obviously, this will result in fewer mechanical components for an apparatus capable of the same amount of output; less bulk of a machine having the same output; the use of two broaches making successive cuts with the second deepening the cut of the first; etc. Various types of feeding operations that can be used utilizing this dual carriage arrangement are subsequently described herein and further specific advantages will become more apparent in connection with those descriptions.
Another factor that contributes substantially to the advantageous use of embodiments of the present invention is the release of the broach from the carriage at the end of the cutting stroke and the return of the broach to the carriage after the just-machined workpiece is removed from the position it occupied during the machining stroke. For example, this simplifies the workpiece holder since it is not necessary that it resist forces applied to the workpiece during the return stroke of the broach. This simplification of the workpiece holder also results in a simplification of the feeding of workpieces to the holder and, in many instances, will actually increase the production rate due to less time lost in replacing workpieces. Also, it permits the discharge of the just-machined workpiece to commence almost as the broaching stroke ends rather than awaiting the return of the broach to its initial position before the workpiece removal can commence.
Other objects and advantages of the invention will be apparent to those knowledgeable in the art from the following description and the appended drawings.